Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $34.68   5.541%   $36.6016   $36.60   $36.60   $36.60  
  Purchase #2 $147.39   13.444%   $167.2051   $167.21   $167.20   $167.20  
  Purchase #3 $155.35   6.257%   $165.0702   $165.07   $165.05   $165.10  
  Purchase #4 $109.92   12.198%   $123.328   $123.33   $123.35   $123.30  
  Purchase #5 $235.52   6.109%   $249.9079   $249.91   $249.90   $249.90  
  Purchase #6 $131.95   7.495%   $141.8397   $141.84   $141.85   $141.80  
  Purchase #7 $79.31   5.171%   $83.4111   $83.41   $83.40   $83.40  
  7 purchase totals = $894.12       $967.3636   $967.37   $967.35   $967.30